Elie Wiesel, Holocaust survivor and founding chairman of the United States Holocaust Memorial Council, watches as Barack Obama lights a candle in the Hall of Remembrance at the United States Holocaust Memorial Museum in Washington yesterday.

In a speech, Mr Obama announced new sanctions on people and entities in Iran and Syria that use technology to target citizens and erode their human rights. More broadly, he spoke of the work that "will never be done" – the global challenge of preventing atrocities. He told Mr Wiesel: "You show us the way. If you cannot give up, if you can believe, then we can believe."